1. Field of the Invention
The present invention relates to a multilayer ceramic capacitor.
2. Description of the Related Art
In recent years, with the decreasing size and increasing performance of electronic components, a size reduction and an increased capacitance are required in multilayer ceramic capacitors. Such a multilayer ceramic capacitor includes, for example, a ceramic body with a rectangular parallelepiped shape, in which ceramic layers defining an inner layer portion and internal electrodes are laminated alternately, and ceramic layers defining an outer layer portion are arranged on upper and lower surfaces of the laminated body, and also includes external electrodes formed on opposite end surfaces of the ceramic body.
In order to achieve a size reduction and an increased capacity in the multilayer ceramic capacitor, it is necessary to reduce the thickness and increase the lamination density of the ceramic layers defining the inner layer portion (dielectric ceramic layers) and the internal electrodes as much as possible. However, in a multilayer ceramic capacitor in which the dielectric ceramic layers and the internal electrodes have been reduced in thickness and increased in lamination density, if the thickness of the dielectric ceramic layers is further reduced, the insulation resistance between internal electrodes will decrease, leading to reduced reliability. It has therefore been difficult to achieve a smaller thickness and a higher lamination density while ensuring reliability.
Japanese Patent No. 3,334,607 discloses a dielectric ceramic composition for forming a dielectric ceramic layer, for use in a multilayer ceramic capacitor that takes into account the insulation resistance of a dielectric ceramic layer having a reduced thickness between internal electrodes. In a ceramic body in which internal electrodes and dielectric ceramic layers containing barium titanate as a main component are laminated alternately, the dielectric ceramic composition has the composition represented by the formula: {BaO} mTiO2+αR2O3+βBaZrO3+γMgO+gMnO, where R2O3 is at least one selected from Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, and Yb2O3;
and α, β, γ, and g each represent a molar ratio, and are in the following ranges: 0.001≦α≦0.06; 0.005≦β≦0.06; 0.001<γ≦0.12; 0.001<g≦0.12; γ+g≦0.13; and 1.000<m≦1.035.
However, with the dielectric ceramic composition forming the dielectric ceramic layers in the multilayer ceramic capacitor described in Japanese Patent No. 3,334,607, the reliability significantly decreases in the case of a multilayer ceramic capacitor including regions of dielectric ceramic layers with a reduced thickness (not more than 0.55 μm).